The protection and management of MV/LV transformers in a rural environment requires specific circuit breakers compatible with significant load differences, thus ensuring full exploitation of the installed power, even in unbalanced operation.

Technical characteristics

1- Post circuit breaker with digital trip unit

2 - Digital trip unit

Trip time as per HN 63-S-11 + corrected values (in bold type) to match the selectivity of the TPC fuses.

Description

Circuit breaker unit

These units （4 poles 3 of which are protected） cut off in air with metal partition chambers to break the arc.
When the circuit breaker is open, a contact makes an electrical link between the transformer neutral and the station structural earth.
When the circuit breaker is closed, a spark gap limits the rise in potential of the LV neutral, in relation to the structural earthing, for a value exceeding 10 kV.
The circuit breaker is installed inside a weatherproof GRP case.

Digital Trip Unit

The Digital Trip Unit protects the three ratings of the post-mounted transformer （50 kVA, 100
kVA and 160 kVA）， whether it be a conventional transformer （no internal protection） or a new transformer with protection （TPC）。
The transformer protection rating is set by a selector.

The micro-controller assesses the transformer temperature in real time, based on the currents in the three phases and the external ambient temperature. This ambient temperature is computed based on the probe and a mathematical model that is also a function of the three phase currents.